This invention relates to a mineral mining installation, and in particular to an advance mechanism for a mine roof support unit.
It is known to employ, in a mineral mining installation, hydraulic advance rams for connecting movable roof support units to a scraper-chain conveyor arranged alongside a mineral face. The advance rams are extended and retracted alternately, from time-to-time, to advance the conveyor towards the mineral face, and to draw up the roof support units to follow this conveyor advance movement. In most case, the advance rams are extended and retracted by their full working stroke; but, under certain conditions, it may be necessary to displace the conveyor section (or the roof support unit associated with a given ram) by a distance somewhat less than the full working stroke of the ram. Use can then be made of a device which serves to limit the working stroke of the ram to a distance less than its full working stroke.
For example, U.S. Pat. No. 4,379,424 describes a hydraulic advance ram having a stop member between its cylinder and its piston rod. The stop member partially surrounds the piston rod, and is engageable with the cylinder to vary the working stroke of the ram. However, adjustment of the working stroke of this known type of ram is a relatively complicated matter, particularly in view of the limited amount of space available in a congested mine working.
The aim of the invention is to provide an advance mechanism having a stroke-limiting device which can be adjusted in the simplest possible manner.